when suggesting RUST_BACKTRACE=1, add a special note for Miri's env var isolation

library/std/src/panicking.rs

@@ -277,6 +277,13 @@ fn default_hook(info: &PanicInfo<'_>) {
                         "note: run with `RUST_BACKTRACE=1` environment variable to display a \
                              backtrace"
                     );
+                    if cfg!(miri) {
+                        let _ = writeln!(
+                            err,
+                            "note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` \
+                                for the environment variable to have an effect"
+                        );
+                    }
                 }
             }
             // If backtraces aren't supported or are forced-off, do nothing.

src/tools/miri/tests/fail/function_calls/exported_symbol_bad_unwind1.stderr

@@ -1,6 +1,7 @@
 thread 'main' panicked at $DIR/exported_symbol_bad_unwind1.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 error: Undefined Behavior: unwinding past a stack frame that does not allow unwinding
   --> $DIR/exported_symbol_bad_unwind1.rs:LL:CC
    |

src/tools/miri/tests/fail/function_calls/exported_symbol_bad_unwind2.both.stderr

@@ -1,6 +1,7 @@
 thread 'main' panicked at $DIR/exported_symbol_bad_unwind2.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 thread 'main' panicked at RUSTLIB/core/src/panicking.rs:LL:CC:
 panic in a function that cannot unwind
 stack backtrace:

src/tools/miri/tests/fail/function_calls/exported_symbol_bad_unwind2.definition.stderr

@@ -1,6 +1,7 @@
 thread 'main' panicked at $DIR/exported_symbol_bad_unwind2.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 thread 'main' panicked at RUSTLIB/core/src/panicking.rs:LL:CC:
 panic in a function that cannot unwind
 stack backtrace:

src/tools/miri/tests/fail/function_calls/exported_symbol_bad_unwind2.extern_block.stderr

@@ -1,6 +1,7 @@
 thread 'main' panicked at $DIR/exported_symbol_bad_unwind2.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 error: Undefined Behavior: unwinding past a stack frame that does not allow unwinding
   --> $DIR/exported_symbol_bad_unwind2.rs:LL:CC
    |

src/tools/miri/tests/fail/function_calls/return_pointer_on_unwind.stderr

@@ -1,6 +1,7 @@
 thread 'main' panicked at $DIR/return_pointer_on_unwind.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 error: Undefined Behavior: using uninitialized data, but this operation requires initialized memory
   --> $DIR/return_pointer_on_unwind.rs:LL:CC
    |

src/tools/miri/tests/fail/intrinsics/uninit_uninhabited_type.stderr

@@ -1,6 +1,7 @@
 thread 'main' panicked at RUSTLIB/core/src/panicking.rs:LL:CC:
 aborted execution: attempted to instantiate uninhabited type `!`
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 thread caused non-unwinding panic. aborting.
 error: abnormal termination: the program aborted execution
   --> RUSTLIB/std/src/sys/pal/PLATFORM/mod.rs:LL:CC

src/tools/miri/tests/fail/intrinsics/zero_fn_ptr.stderr

@@ -1,6 +1,7 @@
 thread 'main' panicked at RUSTLIB/core/src/panicking.rs:LL:CC:
 aborted execution: attempted to zero-initialize type `fn()`, which is invalid
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 thread caused non-unwinding panic. aborting.
 error: abnormal termination: the program aborted execution
   --> RUSTLIB/std/src/sys/pal/PLATFORM/mod.rs:LL:CC

src/tools/miri/tests/fail/panic/bad_unwind.stderr

@@ -1,6 +1,7 @@
 thread 'main' panicked at $DIR/bad_unwind.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 error: Undefined Behavior: unwinding past a stack frame that does not allow unwinding
   --> $DIR/bad_unwind.rs:LL:CC
    |

src/tools/miri/tests/fail/panic/double_panic.stderr

@@ -1,6 +1,7 @@
 thread 'main' panicked at $DIR/double_panic.rs:LL:CC:
 first
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 thread 'main' panicked at $DIR/double_panic.rs:LL:CC:
 second
 stack backtrace:

src/tools/miri/tests/fail/panic/panic_abort1.stderr

@@ -1,6 +1,7 @@
 thread 'main' panicked at $DIR/panic_abort1.rs:LL:CC:
 panicking from libstd
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 error: abnormal termination: the program aborted execution
   --> RUSTLIB/panic_abort/src/lib.rs:LL:CC
    |

src/tools/miri/tests/fail/panic/panic_abort2.stderr

@@ -1,6 +1,7 @@
 thread 'main' panicked at $DIR/panic_abort2.rs:LL:CC:
 42-panicking from libstd
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 error: abnormal termination: the program aborted execution
   --> RUSTLIB/panic_abort/src/lib.rs:LL:CC
    |

src/tools/miri/tests/fail/panic/panic_abort3.stderr

@@ -1,6 +1,7 @@
 thread 'main' panicked at $DIR/panic_abort3.rs:LL:CC:
 panicking from libcore
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 error: abnormal termination: the program aborted execution
   --> RUSTLIB/panic_abort/src/lib.rs:LL:CC
    |

src/tools/miri/tests/fail/panic/panic_abort4.stderr

@@ -1,6 +1,7 @@
 thread 'main' panicked at $DIR/panic_abort4.rs:LL:CC:
 42-panicking from libcore
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 error: abnormal termination: the program aborted execution
   --> RUSTLIB/panic_abort/src/lib.rs:LL:CC
    |

src/tools/miri/tests/fail/terminate-terminator.stderr

@@ -3,6 +3,7 @@ warning: You have explicitly enabled MIR optimizations, overriding Miri's defaul
 thread 'main' panicked at $DIR/terminate-terminator.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 thread 'main' panicked at RUSTLIB/core/src/panicking.rs:LL:CC:
 panic in a function that cannot unwind
 stack backtrace:

src/tools/miri/tests/fail/unwind-action-terminate.stderr

@@ -1,6 +1,7 @@
 thread 'main' panicked at $DIR/unwind-action-terminate.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 thread 'main' panicked at RUSTLIB/core/src/panicking.rs:LL:CC:
 panic in a function that cannot unwind
 stack backtrace:

src/tools/miri/tests/panic/div-by-zero-2.stderr

@@ -1,3 +1,4 @@
 thread 'main' panicked at $DIR/div-by-zero-2.rs:LL:CC:
 attempt to divide by zero
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect

src/tools/miri/tests/panic/function_calls/exported_symbol_good_unwind.stderr

@@ -1,6 +1,7 @@
 thread 'main' panicked at $DIR/exported_symbol_good_unwind.rs:LL:CC:
 explicit panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 thread 'main' panicked at $DIR/exported_symbol_good_unwind.rs:LL:CC:
 explicit panic
 thread 'main' panicked at $DIR/exported_symbol_good_unwind.rs:LL:CC:

src/tools/miri/tests/panic/oob_subslice.stderr

@@ -1,3 +1,4 @@
 thread 'main' panicked at $DIR/oob_subslice.rs:LL:CC:
 range end index 5 out of range for slice of length 4
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect

src/tools/miri/tests/panic/overflowing-lsh-neg.stderr

@@ -1,3 +1,4 @@
 thread 'main' panicked at $DIR/overflowing-lsh-neg.rs:LL:CC:
 attempt to shift left with overflow
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect

src/tools/miri/tests/panic/overflowing-rsh-1.stderr

@@ -1,3 +1,4 @@
 thread 'main' panicked at $DIR/overflowing-rsh-1.rs:LL:CC:
 attempt to shift right with overflow
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect

src/tools/miri/tests/panic/overflowing-rsh-2.stderr

@@ -1,3 +1,4 @@
 thread 'main' panicked at $DIR/overflowing-rsh-2.rs:LL:CC:
 attempt to shift right with overflow
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect

src/tools/miri/tests/panic/panic2.stderr

@@ -1,3 +1,4 @@
 thread 'main' panicked at $DIR/panic2.rs:LL:CC:
 42-panicking from libstd
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect

src/tools/miri/tests/panic/panic3.stderr

@@ -1,3 +1,4 @@
 thread 'main' panicked at $DIR/panic3.rs:LL:CC:
 panicking from libcore
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect

src/tools/miri/tests/panic/panic4.stderr

@@ -1,3 +1,4 @@
 thread 'main' panicked at $DIR/panic4.rs:LL:CC:
 42-panicking from libcore
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect

src/tools/miri/tests/panic/transmute_fat2.stderr

@@ -1,3 +1,4 @@
 thread 'main' panicked at $DIR/transmute_fat2.rs:LL:CC:
 index out of bounds: the len is 0 but the index is 0
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect

src/tools/miri/tests/panic/unsupported_foreign_function.stderr

@@ -1,3 +1,4 @@
 thread 'main' panicked at $DIR/unsupported_foreign_function.rs:LL:CC:
 unsupported Miri functionality: can't call foreign function `foo` on $OS
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect

src/tools/miri/tests/panic/unsupported_syscall.stderr

@@ -1,3 +1,4 @@
 thread 'main' panicked at $DIR/unsupported_syscall.rs:LL:CC:
 unsupported Miri functionality: can't execute syscall with ID 0
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect

src/tools/miri/tests/pass/panic/catch_panic.stderr

@@ -1,6 +1,7 @@
 thread 'main' panicked at $DIR/catch_panic.rs:LL:CC:
 Hello from std::panic
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 Caught panic message (&str): Hello from std::panic
 thread 'main' panicked at $DIR/catch_panic.rs:LL:CC:
 Hello from std::panic: 1

src/tools/miri/tests/pass/panic/concurrent-panic.stderr

@@ -3,6 +3,7 @@ Thread 1 reported it has started
 thread '<unnamed>' panicked at $DIR/concurrent-panic.rs:LL:CC:
 panic in thread 2
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 Thread 2 blocking on thread 1
 Thread 2 reported it has started
 Unlocking mutex

src/tools/miri/tests/pass/panic/nested_panic_caught.stderr

@@ -1,6 +1,7 @@
 thread 'main' panicked at $DIR/nested_panic_caught.rs:LL:CC:
 once
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 thread 'main' panicked at $DIR/nested_panic_caught.rs:LL:CC:
 twice
 stack backtrace:

src/tools/miri/tests/pass/panic/thread_panic.stderr

@@ -1,5 +1,6 @@
 thread '<unnamed>' panicked at $DIR/thread_panic.rs:LL:CC:
 Hello!
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+note: in Miri, you may have to set `-Zmiri-env-forward=RUST_BACKTRACE` for the environment variable to have an effect
 thread 'childthread' panicked at $DIR/thread_panic.rs:LL:CC:
 Hello, world!